The present invention relates to a method and a device for operating an actuating drive in a motor vehicle. Devices of this kind are used for controlling the actuating drives of window lifters, sliding sunroofs, etc.
Such a method and device, respectively, are described in German Patent No. 19615123. To be more precise, this document deals with a device and a method for electronically monitoring an actuating drive mounted in a vehicle, the device monitoring an actuating force exerted by the actuating drive to prevent the actuating force from exceeding a limiting value. The aim is to prevent injury to a person caught in the closing area of the window or sliding sunroof operated by the actuating drive, or damage to the actuating drive. In this context, the problem arises that external shocks which the vehicle is subject to, for example, due to unevenness of the road being driven on, interfere with the measurement of the actuating force by inducing inertial forces in the actuating drive or in the part actuated thereby.
According to German Patent No. 19615123, the intention is for this problem to be solved by using the speedometer signal of the vehicle as input variable for the control of the actuating drive, namely in that a higher limiting value is input while the vehicle is being driven than while the vehicle is at rest.
However, this approach is not completely satisfactory. The moments of inertia induced by shocks can reach considerable levels. To prevent the closing-force limiter from responding incorrectly because of such a shock, the limiting value must be selected considerably higher while the vehicle is being driven than is desirable for effectively protecting persons from injuries.
A further method and a device for operating an actuating drive in a motor vehicle are known from German Patent No. 4000730. In the case of this method and this device, provision is made to acquire a characteristic quantity having a relation to the actuating force of the part driven by the actuating drive, and to measure the path covered by the part. On the basis of this data, the characteristic quantity is differentiated with respect to path. The value of this derivative is monitored, and the actuating drive is reversed or stopped when a limiting value of the derivative is exceeded.
In this device, the exceeding of the limiting value which results in the stopping or in the reversing of the actuating drive does not necessarily coincide with the exceeding of a maximum closing force. Besides, the derivative necessarily responds to fast changes in force, as are caused in particular by exterior shocks, in a significantly more sensitive manner as the characteristic quantity from which it is calculated. To compensate for this, signal filtering is required in determining the curve of the characteristic quantity.
The present invention provides a method and a device, respectively, for operating an actuating drive, allowing disturbances due to shocks to be suppressed in a manner adapted to the motional condition of the motor vehicle while complying with fixed limiting values of the exerted actuating force at the same time. This is achieved in that, to suppress fast changes in the actuating force which are caused by shocks, different filtering methods are used as a function of the motional condition of the motor vehicle, it being possible for the suppression to be weaker while the vehicle is at rest because of the lower probability of shocks than while the vehicle is being driven, or to be completely omitted.
The ignition of the motor vehicle can be easily used as a criterion for changing between the two filtering methods.
The first filtering method, which is used while the vehicle is being driven or while the engine of the vehicle is running, preferably filters out increases in the actuating force which exceed 20 N/mm. Changes in the actuating force which are due to an exterior shock generally manifest themselves by fast changes in the actuating force. Taking a spring rate of 20 N/mm as a basis, the device according to the present invention is moreover capable of observing the increase in the actuating force over a travel of at least 5 mm before a maximum force of 100 N is reached, at which the actuating drive shall reverse according to the legal regulation. A great number of force-measuring values can be taken on these 5 mm so that the exerted force can be exactly estimated, possibly by messaging, interpolation, etc., even under the influence of external disturbances.
A significantly higher spring rate of 65 N/mm can be used when the vehicle is at rest. In such conditions, the filtered signal can increase from 0 to 100 N over a length of travel of 1.3 mm. However, since substantially no shocks are to be expected while the vehicle is at rest, it is less important to acquire a great number of measuring values for the purpose of averaging fluctuations. In this case, therefore, the length of travel is sufficient for an accurate measurement.